Catalyst, its preparation and use

ABSTRACT

A dehydrogenation catalyst is described comprising an iron oxide, an alkali metal or compound thereof, and silver or a compound thereof. Further a process is described for preparing a dehydrogenation catalyst that comprises preparing a mixture of iron oxide, an alkali metal or compound thereof, and silver or a compound thereof and calcining the mixture. A process for dehydrogenating a dehydrogenatable hydrocarbon and a process for polymerizing the dehydrogenated hydrocarbon are also described.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application Ser.No. 60/915,853 filed May 3, 2007, the entire disclosure of which isherein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a catalyst, a process for preparing thecatalyst, and a process for the dehydrogenation of a dehydrogenatablehydrocarbon.

BACKGROUND

Dehydrogenation catalysts and the preparation of such catalysts areknown in the art. Iron oxide based catalysts are customarily used in thedehydrogenation of dehydrogenatable hydrocarbons to yield, among othercompounds, a corresponding dehydrogenated hydrocarbon. In this field ofcatalytic dehydrogenation of dehydrogenatable hydrocarbons todehydrogenated hydrocarbons there are ongoing efforts to developdehydrogenation catalysts that exhibit improved performance.

EP 1027928 discloses dehydrogenation catalysts based upon an iron oxidemade by spray roasting an iron salt solution, and adding additionalcatalyst components selected from the group consisting of Be, Mg, Ca,Sr, Ba, Sc, Ti, Zr, Hf, V, Ta, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir,Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Tl, Na, Cs, La, Li, Ge,Sn, Pb, Bi, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.These catalysts generally have one or more potassium compounds.

SUMMARY OF THE INVENTION

The present invention provides a dehydrogenation catalyst comprising aniron oxide, an alkali metal or compound thereof, and silver or acompound thereof.

In a preferred embodiment, the invention provides a dehydrogenationcatalyst comprising an iron oxide, an alkali metal or compound thereof,and silver or a compound thereof wherein the silver or compound thereofis present in an amount of at least about 0.01 millimoles of silver permole of iron oxide, calculated as Fe₂O₃.

In another preferred embodiment, the invention provides adehydrogenation catalyst comprising iron oxide, an alkali metal orcompound thereof, silver and silver ferrite.

In another preferred embodiment, the invention provides adehydrogenation catalyst comprising iron oxide, potassium or a compoundthereof, cerium or a compound thereof, calcium or a compound thereof,molybdenum or a compound thereof and silver.

The present invention further provides a process for preparing adehydrogenation catalyst comprising preparing a mixture comprising aniron oxide, an alkali metal or compound thereof, and silver or acompound thereof wherein the silver or compound thereof is present in anamount of at least about 0.01 millimoles of silver per mole of ironoxide calculated as Fe₂O₃ and calcining the mixture.

The present invention provides a process for preparing a dehydrogenationcatalyst comprising preparing a mixture of iron oxide, potassium or acompound thereof, cerium or a compound thereof, calcium or a compoundthereof, molybdenum or a compound thereof and silver and calcining themixture.

The present invention also provides a process for dehydrogenating adehydrogenatable hydrocarbon comprising contacting a feed comprising adehydrogenatable hydrocarbon with a catalyst comprising an iron oxide,an alkali metal or compound thereof, and silver or a compound thereofwherein the silver is present in an amount of at least about 0.01millimoles of silver per mole of iron oxide, calculated as Fe₂O₃.

The present invention further provides a process for dehydrogenating adehydrogenatable hydrocarbon comprising contacting a feed comprising adehydrogenatable hydrocarbon with a catalyst comprising iron oxide,potassium or a compound thereof, cerium or a compound thereof, calciumor a compound thereof, molybdenum or a compound thereof and silver.

The present invention still further provides a method of using adehydrogenated hydrocarbon for making polymers or copolymers, comprisingpolymerizing the dehydrogenated hydrocarbon to form a polymer orcopolymer comprising monomer units derived from the dehydrogenatedhydrocarbon, wherein the dehydrogenated hydrocarbon has been prepared ina process for the dehydrogenation of a dehydrogenatable hydrocarbon asdescribed above.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a catalyst that satisfies the need forimproved dehydrogenation catalysts. The catalyst comprises an ironoxide, an alkali metal or compound thereof, and silver or a compoundthereof. The catalyst comprising silver is more active and/or moreselective than a similar catalyst that does not contain silver.Additionally, using this catalyst in the dehydrogenation of ethylbenzeneto styrene may result in a reduced amount of α-methyl styrene in theproduct stream.

The dehydrogenation catalyst is an iron oxide based catalyst. Inaddition, the iron may be present in the form of potassium ferrite or asa compound with any of the other catalyst components including silver.The catalyst comprises from 10 to 90 wt % iron oxide, calculated asFe₂O₃. The catalyst preferably comprises from 40 to 85 wt % iron oxide,and more preferably comprises from 60 to 80 wt % iron oxide.

The iron oxide may be formed or processed by any process known to thoseskilled in the art. Additionally, the catalyst may comprise one or moretypes of iron oxide. The iron oxide may be formed by heat decompositionof iron halide to form iron oxide as described in U.S. PatentApplication Publication 2003/0144566, which is hereinafter referred toas regenerator iron oxide. The regenerator iron oxide may optionally betreated to reduce the residual halide content in the iron oxide to atmost 2000 ppm or preferably at most 1500 ppm. The iron oxide may beformed by spray roasting of iron chloride in the presence of Column 6metals or hydrolyzable metal chlorides. In the alternative, the ironoxide may be formed by a precipitation process. The iron oxide may berestructured by heating in the presence of a restructuring agent beforeits use in the catalyst by the process described in U.S. Pat. No.5,668,075 and U.S. Pat. No. 5,962,757. The iron oxide may be treated,washed or heat conditioned before its use in this catalyst as describedin U.S. Pat. No. 5,401,485. The iron oxide may be red, yellow, or blackiron oxide. Yellow iron oxide is a hydrated iron oxide typicallydepicted as Fe₂O₃.H₂O or α-FeOOH. When yellow iron oxide is added, atleast 5 wt %, or preferably at least 10 wt % of the total iron oxide inthe catalyst, calculated as Fe₂O₃, may be yellow iron oxide, and at most50 wt % of the total iron oxide may be yellow iron oxide. An example ofa red iron oxide can be made by calcination of a yellow iron oxide madeby the Penniman method. Iron oxide-providing compounds that may bepresent in the catalyst include goethite, hematite, magnetite,maghemite, and lepidocricite.

The catalyst also comprises an alkali metal selected from the group ofalkali metals including lithium, sodium, potassium, rubidium, cesium andfrancium, and is preferably potassium. One or more of these metals maybe used. The alkali metal may be present in the catalyst as a compoundof an alkali metal. The alkali metals are generally present in a totalquantity of at least 0.2 moles, preferably at least 0.25 moles, morepreferably at least 0.45 moles, and most preferably at least 0.55 moles,per mole of iron oxide, calculated as Fe₂O₃. The alkali metals aregenerally present in a quantity of at most 5 moles, or preferably atmost 1 mole, per mole of iron oxide. The alkali metal compound mayinclude hydroxides; carbonates; bicarbonates; carboxylates, for example,formates, acetates, oxalates and citrates; nitrates; and oxides. Thepreferred alkali metal compound is potassium carbonate.

The catalyst also comprises silver that may be present as any compoundof silver, for example silver oxide and silver ferrite or it may bepresent as silver metal. The silver may be added as silver ferrite,silver carbonate, silver nitrate, silver oxide, silver chromate, silveroxalate, silver powder, silver nanoparticles, or silver metal. Inaddition, silver compounds may convert to silver ferrite or other silvercompounds during catalyst formation. The silver is generally present ina total quantity of at least 0.5 millimoles, preferably at least 1millimole and more preferably at least 2.5 millimoles, and mostpreferably at least 10 millimoles per mole of iron oxide calculated asFe₂O₃. The silver is generally present in a total quantity of at most 1mole, and preferably at most 0.5 moles per mole of iron oxide.

The catalyst may further comprise a lanthanide. The lanthanide isselected from the group of lanthanides of atomic number in the range offrom 57 to 66 inclusive. The lanthanide is preferably cerium. Thelanthanide may be present as a compound of a lanthanide. The lanthanideis generally present in a total quantity of at least 0.02 moles,preferably at least 0.05 moles, more preferably at least 0.06 moles permole of iron oxide, calculated as Fe₂O₃. The lanthanide is generallypresent in a total quantity of at most 0.2 moles, preferably at most0.15 moles, more preferably at most 0.14 moles per mole of iron oxide.The lanthanide compound may include hydroxides; carbonates;bicarbonates; carboxylates, for example, formates, acetates, oxalatesand citrates; nitrates; and oxides. The preferred lanthanide compound iscerium carbonate.

The catalyst may further comprise an alkaline earth metal or compoundthereof. The alkaline earth metal may be calcium or magnesium, and it ispreferably calcium. The alkaline earth metal compound is generallypresent in a quantity of at least 0.01 moles, and preferably at least0.02 moles per mole of iron oxide calculated as Fe₂O₃. The alkalineearth metal compound is generally present in a quantity of at most 1mole, and preferably at most 0.2 moles per mole of iron oxide.

The catalyst may further comprise a Column 6 metal or compound thereof.The Column 6 metal may be molybdenum or tungsten, and it is preferablymolybdenum. The Column 6 metal is generally present in a quantity of atleast 0.01 moles, preferably at least 0.02 moles per mole of iron oxide,calculated as Fe₂O₃. The Column 6 metal is generally present in aquantity of at most 0.5 moles, preferably at most 0.1 moles per mole ofiron oxide.

Additional catalyst components that may be combined with the iron oxideinclude metals and compounds thereof selected from the group consistingof: Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mn, Tc, Re, Ru, Os, Co, Rh, Ir,Ni, Pd, Pt, Cu, Au, Zn, Cd, Hg, Al, Ga, In, Ti, Si, Ge, Sn, Pb, P, As,Sb, Bi, S, Se and Te. These components may be added by any method knownto those skilled in the art. The additional catalyst components mayinclude hydroxides; bicarbonates; carbonates; carboxylates, for exampleformates, acetates, oxalates and citrates; nitrates; and oxides.Palladium, platinum, ruthenium, rhodium, iridium, copper, and chromiumare preferred additional catalyst components.

The catalyst may be prepared by any method known to those skilled in theart. For example, a paste may be formed comprising iron oxide, alkalimetal or a compound thereof, silver or a compound thereof and anyadditional catalyst component(s). A mixture of these catalyst componentsmay be mulled and/or kneaded or a homogenous or heterogeneous solutionof any of these components may be impregnated on the iron oxide.Sufficient quantities of each component may be calculated from thecomposition of the catalyst to be prepared. Examples of applicablemethods can be found in U.S. Pat. No. 5,668,075; U.S. Pat. No.5,962,757; U.S. Pat. No. 5,689,023; U.S. Pat. No. 5,171,914; U.S. Pat.No. 5,190,906, U.S. Pat. No. 6,191,065, and EP 1027928, which are hereinincorporated by reference.

In forming the catalyst, a mixture comprising iron oxide, alkali metalor a compound thereof, silver or a compound thereof and any additionalcatalyst component(s) may be shaped into pellets of any suitable form,for example, tablets, spheres, pills, saddles, trilobes, twistedtrilobes, tetralobes, rings, stars, hollow and solid cylinders, andasymmetrically lobed particles as described in U.S. Patent ApplicationPublication 2005/0232853. The addition of a suitable quantity of water,for example up to 30 wt %, typically from 2 to 20 wt %, calculated onthe weight of the mixture, may facilitate the shaping into pellets. Ifwater is added, it may be at least partly removed prior to calcination.Suitable shaping methods are pelletizing, extrusion, and pressing.Instead of pelletizing, extrusion or pressing, the mixture may besprayed or spray dried to form a catalyst. If desired, spray drying maybe extended to include pelletization and calcination.

An additional compound may be combined with the mixture that acts as anaid to the process of shaping and/or extruding the catalyst, for examplea saturated or unsaturated fatty acid (such as palmitic acid, stearicacid, or oleic acid) or a salt thereof, a polysaccharide derived acid ora salt thereof, or graphite, starch, or cellulose. Any salt of a fattyacid or polysaccharide derived acid may be applied, for example anammonium salt or a salt of any metal mentioned hereinbefore. The fattyacid may comprise in its molecular structure from 6 to 30 carbon atoms(inclusive), preferably from 10 to 25 carbon atoms (inclusive). When afatty acid or polysaccharide derived acid is used, it may combine with ametal salt applied in preparing the catalyst, to form a salt of thefatty acid or polysaccharide derived acid. A suitable quantity of theadditional compound is, for example, up to 1 wt %, in particular 0.001to 0.5 wt %, relative to the weight of the mixture.

After formation, the catalyst mixture may be dried and calcined. Dryinggenerally comprises heating the catalyst at a temperature of from about30° C. to about 500° C., preferably from about 100° C. to about 300° C.Drying times are generally from about 2 minutes to 5 hours, preferablyfrom about 5 minutes to about 1 hour. Calcination generally comprisesheating the catalyst, typically in an inert, for example nitrogen orhelium or an oxidizing atmosphere, for example an oxygen containing gas,air, oxygen enriched air or an oxygen/inert gas mixture. The calcinationtemperature is typically at least about 600° C., or preferably at leastabout 700° C., more preferably at least 825° C., and most preferably atleast 880° C. The calcination temperature will typically be at mostabout 1600° C., or preferably at most about 1300° C. Typically, theduration of calcination is from 5 minutes to 12 hours, more typicallyfrom 10 minutes to 6 hours.

The catalyst formed according to the invention may exhibit a wide rangeof physical properties. The surface structure of the catalyst, typicallyin terms of pore volume, median pore diameter and surface area, may bechosen within wide limits. The surface structure of the catalyst may beinfluenced by the selection of the temperature and time of calcination,and by the application of an extrusion aid.

Suitably, the pore volume of the catalyst is at least 0.01 ml/g, moresuitably at least 0.05 ml/g. Suitably, the pore volume of the catalystis at most 0.5, preferably at most 0.4 ml/g, more preferably at most 0.3ml/g, and most preferably at most 0.2 ml/g. Suitably, the median porediameter of the catalyst is at least 500 Å, in particular at least 1000Å. Suitably, the median pore diameter of the catalyst is at most 20000Å, in particular at most 15000 Å. In a preferred embodiment, the medianpore diameter is in the range of from 2000 to 10000 Å. As used herein,the pore volumes and median pore diameters are as measured by mercuryintrusion according to ASTM D4282-92, to an absolute pressure of 6000psia (4.2×10⁷ Pa) using a Micromeretics Autopore 9420 model; (1300contact angle, mercury with a surface tension of 0.473 N/m). As usedherein, median pore diameter is defined as the pore diameter at which50% of the mercury intrusion volume is reached.

The surface area of the catalyst is preferably in the range of from 0.01to 20 m²/g, more preferably from 0.1 to 10 m²/g.

The crush strength of the catalyst is suitably at least 10 N/mm, andmore suitably it is in the range of from 20 to 100 N/mm, for exampleabout 55 or 60 N/mm.

In another aspect, the present invention provides a process for thedehydrogenation of a dehydrogenatable hydrocarbon by contacting adehydrogenatable hydrocarbon and steam with an iron oxide based catalystmade according to the invention to produce the correspondingdehydrogenated hydrocarbon.

The dehydrogenated hydrocarbon formed by the dehydrogenation process isa compound having the general formula:

R¹R²C═CH₂

wherein R¹ and R² independently represent an alkyl, alkenyl or a phenylgroup or a hydrogen atom.

The dehydrogenatable hydrocarbon is a compound having the generalformula:

R¹R²HC—CH₃

wherein R¹ and R² independently represent an alkyl, alkenyl or a phenylgroup or a hydrogen atom.

A suitable phenyl group may have one or more methyl groups assubstitutes. A suitable alkyl group generally has from 2 to 20 carbonatoms per molecule, and preferably from 3 to 8 carbon atoms such as inthe case of n-butane and 2-methylbutane. Suitable alkyl substituents arepropyl (—CH₂—CH₂—CH₃), 2-propyl (i.e., 1-methylethyl, —CH(—CH₃)₂), butyl(—CH₂—CH₂—CH₂—CH₃), 2-methyl-propyl (—CH₂—CH(—CH₃)₂), and hexyl(—CH₂—CH₂—CH₂—CH₂—CH₂—CH₃), in particular ethyl (—CH₂—CH₃). A suitablealkenyl group generally has from about 4 to about 20 carbon atoms permolecule, and preferably from 4 to 8 carbon atoms per molecule.

The dehydrogenatable hydrocarbon may be an alkyl substituted benzene,although other aromatic compounds may be applied as well, such as alkylsubstituted naphthalene, anthracene, or pyridine. Examples of suitabledehydrogenatable hydrocarbons are butyl-benzene, hexylbenzene,(2-methylpropyl)benzene, (1-methylethyl)benzene (i.e., cumene),1-ethyl-2-methyl-benzene, 1,4-diethylbenzene, ethylbenzene, 1-butene,2-methylbutane and 3-methyl-1-butene. It is possible to convert n-butanewith the present process via 1-butene into 1,3-butadiene and2-methylbutane via tertiary amylenes into isoprene.

Examples of dehydrogenated hydrocarbons that can be produced by theprocess are butadiene, alpha-methyl styrene, divinylbenzene, isopreneand styrene.

The dehydrogenation process is frequently a gas phase process; wherein agaseous feed comprising the reactants is contacted with the solidcatalyst. The catalyst may be present in the form of a fluidized bed ofcatalyst particles or in the form of a packed bed. The process may becarried out as a batch process or as a continuous process. Hydrogen maybe a further product of the dehydrogenation process, and thedehydrogenation in question may be a non-oxidative dehydrogenation.Examples of applicable methods for carrying out the dehydrogenationprocess can be found in U.S. Pat. No. 5,689,023; U.S. Pat. No.5,171,914; U.S. Pat. No. 5,190,906; U.S. Pat. No. 6,191,065, and EP1027928, which are herein incorporated by reference.

It is advantageous to apply water, which may be in the form of steam, asan additional component of the feed. The presence of water will decreasethe rate of deposition of coke on the catalyst during thedehydrogenation process. Typically the molar ratio of water to thedehydrogenatable hydrocarbon in the feed is in the range of from 1 to50, more typically from 3 to 30, for example from 5 to 10.

The dehydrogenation process is typically carried out at a temperature inthe range of from 500 to 700° C., more typically from 550 to 650° C.,for example 600° C., or 630° C. In one embodiment, the dehydrogenationprocess is carried out isothermally. In other embodiments, thedehydrogenation process is carried out in an adiabatic manner, in whichcase the temperatures mentioned are reactor inlet temperatures, and asthe dehydrogenation progresses the temperature may decrease typically byup to 150° C., more typically by from 10 to 120° C. The absolutepressure is typically in the range of from 10 to 300 kPa, more typicallyfrom 20 to 200 kPa, for example 50 kPa, or 120 kPa.

If desired, one, two, or more reactors, for example three or four, maybe applied. The reactors may be operated in series or parallel. They mayor may not be operated independently from each other, and each reactormay be operated under the same conditions or under different conditions.

When operating the dehydrogenation process as a gas phase process usinga packed bed reactor, the LHSV may preferably be in the range of from0.01 to 10 h⁻¹, more preferably in the range of from 0.1 to 2 h⁻¹. Asused herein, the term “LHSV” means the Liquid Hourly Space Velocity,which is defined as the liquid volumetric flow rate of the hydrocarbonfeed, measured at normal conditions (i.e., 0° C. and 1 bar absolute),divided by the volume of the catalyst bed, or by the total volume of thecatalyst beds if there are two or more catalyst beds.

The conditions of the dehydrogenation process may be selected such thatthe conversion of the dehydrogenatable hydrocarbon is in the range offrom 20 to 100 mole %, preferably from 30 to 80 mole %, or morepreferably from 35 to 75 mole %.

The activity (T70) of the catalyst is defined as the temperature undergiven operating conditions at which the conversion of thedehydrogenatable hydrocarbon in a dehydrogenation process is 70 mole %.A more active catalyst thus has a lower T70 than a less active catalyst.The corresponding selectivity (S70) is defined as the selectivity to thedesired product at the temperature at which conversion is 70 mole %.

The dehydrogenated hydrocarbon may be recovered from the product of thedehydrogenation process by any known means. For example, thedehydrogenation process may include fractional distillation or reactivedistillation. If desirable, the dehydrogenation process may include ahydrogenation step in which at least a portion of the product issubjected to hydrogenation by which at least a portion of any byproductsformed during dehydrogenation, are converted into the dehydrogenatedhydrocarbon. The portion of the product subjected to hydrogenation maybe a portion of the product that is enriched in the byproducts. Suchhydrogenation is known in the art. For example, the methods known fromU.S. Pat. No. 5,504,268; U.S. Pat. No. 5,156,816; and U.S. Pat. No.4,822,936, which are incorporated herein by reference, are readilyapplicable to the present invention.

One preferred embodiment of a dehydrogenation process is thenonoxidative dehydrogenation of ethylbenzene to form styrene. Thisembodiment generally comprises feeding a feed comprising ethylbenzeneand steam to a reaction zone containing catalyst at a temperature offrom about 500° C. to about 700° C. Steam is generally present in thefeed at a steam to hydrocarbon molar ratio of from about 7 to about 15.In the alternative this process may be carried out at a lower steam tohydrocarbon molar ratio of from about 1 to about 7, preferably of fromabout 2 to about 6. This process typically produces small amounts ofbyproducts, for example phenylacetylene and alpha-methyl styrene, inaddition to styrene. Alpha-methyl styrene is an undesired byproductbecause it acts as a chain terminator when the styrene is laterpolymerized.

Another preferred embodiment of a dehydrogenation process is theoxidative dehydrogenation of ethylbenzene to form styrene. Thisembodiment generally comprises feeding ethylbenzene and an oxidant, forexample, oxygen, iodide, sulfur, sulfur dioxide, or carbon dioxide to areaction zone containing catalyst at a temperature of from about 500° C.to about 800° C. The oxidative dehydrogenation reaction is exothermic sothe reaction can be carried out at lower temperatures and/or lower steamto oil ratios.

Another preferred embodiment of a dehydrogenation process is thedehydrogenation of isoamylenes to form isoprene. This embodimentgenerally comprises feeding a mixed isoamylene feed comprising2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene into areaction zone containing catalyst at a temperature of from about 525° C.to about 675° C. The process is typically conducted at atmosphericpressure. Steam is generally added to the feed at a steam to hydrocarbonmolar ratio of from about 13.5 to about 31.

Another preferred embodiment of a dehydrogenation process is thedehydrogenation of butene to form butadiene. This embodiment generallycomprises feeding a mixed butylenes feed comprising 1-butene and2-butene (cis and/or trans isomers) to a reaction zone containingcatalyst at a temperature of from about 500° C. to about 700° C.

Due to the endothermic nature of most of these dehydrogenationprocesses, additional heat input is often desirable to maintain therequired temperatures to maintain conversion and selectivity. The heatcan be added before a reaction zone, between reaction zones when thereare two or more zones, or directly to the reaction zone.

A preferred embodiment of a suitable heating method is the use of aconventional heat exchanger. The process stream may be heated beforeentering the first or any subsequent reactors. Preferred sources of heatinclude steam and other heated process streams.

Another preferred embodiment of a suitable heating method is the use ofa flameless distributed combustion heater system as described in U.S.Pat. No. 7,025,940, which is herein incorporated by reference.

Another preferred embodiment of a suitable heating method is catalyticor noncatalytic oxidative reheat. Embodiments of this type of heatingmethod are described in U.S. Pat. No. 4,914,249; U.S. Pat. No.4,812,597; and U.S. Pat. No. 4,717,779; which are herein incorporated byreference.

The dehydrogenated hydrocarbon produced by the dehydrogenation processmay be used as a monomer in polymerization processes andcopolymerization processes. For example, the styrene obtained may beused in the production of polystyrene and styrene/diene rubbers. Theimproved catalyst performance achieved by this invention with a lowercost catalyst leads to a more attractive process for the production ofthe dehydrogenated hydrocarbon and consequently to a more attractiveprocess which comprises producing the dehydrogenated hydrocarbon and thesubsequent use of the dehydrogenated hydrocarbon in the manufacture ofpolymers and copolymers which comprise monomer units of thedehydrogenated hydrocarbon. For applicable polymerization catalysts,polymerization processes, polymer processing methods and uses of theresulting polymers, reference is made to H. F. Marks, et al. (ed.),“Encyclopedia of Polymer Science and Engineering”, 2^(nd) Edition, newYork, Volume 16, pp 1-246, and the references cited therein.

The following examples are presented to illustrate the invention, butthey should not be construed as limiting the scope of the invention.

EXAMPLE 1 (COMPARATIVE)

A catalyst was prepared by combining: 900 g iron oxide (Fe₂O₃) (made byheat decomposition of iron chloride) that contained 0.08 wt % Cl and hada surface area of 3.2 m²/g and 100 g yellow iron oxide (FeOOH) withsufficient potassium carbonate, cerium carbonate (as hydrated Ce₂(CO₃)₃containing 52 wt % Ce), molybdenum trioxide, and calcium carbonate togive a catalyst with 18 mmoles Mo per mole of iron oxide and the othercomponents as shown in Table 1. Water (about 10 wt %, relative to theweight of the dry mixture) was added to form a paste, and the paste wasextruded to form 3 mm diameter cylinders that were then cut into 6 mmlengths. The pellets were dried in air at 170° C. for 15 minutes andsubsequently calcined in air at 888° C. for 1 hour. The composition ofthe catalyst after calcination is shown in Table 1 as millimoles permole of iron oxide, calculated as Fe₂O₃.

A 100 cm³ sample of the catalyst was used for the preparation of styrenefrom ethylbenzene under isothermal testing conditions in a reactordesigned for continuous operation. The conditions were as follows:absolute pressure 76 kPa, steam to ethylbenzene molar ratio 10, and LHSV0.65 h⁻¹. In this test, the temperature was initially held at 595° C.for a period of about 5-10 days. The temperature was later adjusted suchthat a 70 mole % conversion of ethylbenzene was achieved (T70). Theselectivity (S70) to styrene at the selected temperature was measured.

EXAMPLES 2-17

Catalysts were prepared according to the invention. The ingredientsdescribed in Example 1 were used. Some of the examples used differentamounts of these ingredients as shown by the catalyst compositions inTable 1. Additionally the calcination temperatures are shown in Table 1because some of the catalysts were calcined at different temperatures.The catalysts of examples 2-17 contained silver that was added in theform of silver oxide in different amounts. The catalysts were testedunder the same conditions as the catalyst of Example 1, and the catalystperformance is shown in Table 1.

TABLE 1 Composition, millimoles/mole Exam- of iron oxide Calc. T70 S70ple Ag Mo Ce Ca K T ° C. ° C. % 1 0 18 100 25 623 888 593.5 95.0 (Comp)2 25.7 18 100 25 623 888 590.1 95.6 3 135 18 100 25 623 888 588.4 95.3 4244.3 18 100 25 623 888 589.5 95.4 5 70 18 75 25 623 800 586.3 95.0 6 7018 75 25 623 975 591.8 96.0 7 200 18 75 25 623 800 590.2 94.8 8 200 1875 25 623 975 596.0 95.6 9 70 18 125 25 623 800 585.8 94.3 10 70 18 12525 623 975 585.9 95.9 11 200 18 125 25 623 800 585.2 94.6 12 200 18 12525 623 975 588.2 95.8 13 135 18 142 25 623 740 584.4 93.9 14 135 18 10025 623 1035 588.5 96.2 15 135 18 100 75 623 888 590.3 95.9 16 135 18 10025 675 888 586.8 95.5 17 135 18 100 25 575 888 589.5 95.3

As can be seen from Examples 1-4, a catalyst having the same ingredientsand being calcined at the same temperature is more active and moreselective if it contains silver. Examples 5-12 show the affects ofchanging the amount of cerium and the calcination temperature of thecatalyst. Examples 13 and 14 show catalysts that were calcined atdifferent temperatures, with the catalyst of Example 13 being calcinedat 740° C., and the catalyst of Example 14 being calcined at 1035° C.Examples 15-17 demonstrate the effect on catalyst performance ofchanging the amount of calcium and potassium in the catalyst.

EXAMPLES 18 (COMPARATIVE) AND 19

Examples 18-19 demonstrate the catalyst performance observed when theiron oxide used is not the same as that used in Examples 1-17. InExample 18, a catalyst was prepared using red iron oxide made by theheat treatment of a precipitated yellow iron oxide. The surface area ofthe red iron oxide was 5.1 m²/g and the red iron oxide contained lessthan 10 ppmw of chloride. The yellow iron oxide was made from oxidationof iron sulfate. The following ingredients were combined: 1000 g of theabove described iron oxide, sufficient potassium carbonate, ceriumcarbonate (as hydrated Ce₂(CO₃)₃ containing 52 wt % Ce), molybdenumtrioxide, and calcium carbonate to give the composition shown in Table2. Water (about 10 wt %, relative to the weight of the dry mixture) wasadded to form a paste, and the paste was extruded to form 3 mm diametercylinders that were then cut into 6 mm lengths. The pellets were driedin air at 170° C. for 15 minutes and subsequently calcined in air at875° C. for 1 hour. The catalyst of Example 19 was prepared in the samemanner as that of Example 18, except that silver oxide was added to givethe composition shown in Table 2. The catalyst performance of thecatalysts of Examples 18 and 19 were tested using the same method as inExamples 1-17, except the temperature was initially held at 600° C. Theresults are shown in Table 2.

EXAMPLES 20 (COMPARATIVE) AND 21

Examples 20-21 demonstrate the catalyst performance observed whenregenerator iron oxide made by heat decomposition is used as in Examples1-17, but it is restructured before its use in the catalyst as describedabove. In Example 20, a mixture was prepared by calcining 1000 g ofregenerator iron oxide with sufficient molybdenum trioxide at 995° C. toproduce a restructured iron oxide composition comprising 19.5 millimoleof molybdenum per mole of iron oxide, calculated as Fe₂O₃. Therestructured iron oxide composition was combined with sufficientpotassium carbonate, cerium carbonate (as hydrated Ce₂(CO₃)₃ containing52 wt % Ce), and calcium carbonate to give the composition shown inTable 2. Water (about 5 wt %, relative to the weight of the dry mixture)was added to form a paste, and the paste was extruded to form 3 mmdiameter cylinders that were then cut into 6 mm lengths. The pelletswere dried in air at 170° C. for 15 minutes and subsequently calcined inair at 775° C. for 1 hour. The composition of the catalyst aftercalcination is shown in Table 2. The catalyst of Example 21 was preparedin the same manner as that of Example 20, except that silver oxide wasadded along with the potassium, cerium and calcium carbonates to givethe composition shown in Table 2. The catalysts of Examples 20 and 21were tested using the same method as in Examples 1-17, except thetemperature was initially held at 600° C. The results are shown in Table2.

TABLE 2 Composition, millimoles/mole Exam- of iron oxide Calc. T70 S70ple Ag Mo Ce Ca K T ° C. ° C. % 18 0 11 89 67 623 875 588.9 94.6 (Comp)19 70 11 89 67 623 875 590.5 95.3 20 0 19.5 96 25 612 775 594.6 95.3(Comp) 21 70 19.5 96 25 612 775 587.9 95.6

As can be seen from Examples 18-19, a non-regenerator iron oxide basedcatalyst that has silver is more selective than a similar catalyst thatdoes not have silver. As can be seen from Examples 20-21, a restructurediron oxide based catalyst that has silver is more active and moreselective than a similar catalyst that does not have silver.

EXAMPLES 22 (COMPARATIVE) AND 23-27

Catalysts were prepared according to the process of Examples 1-17. Theingredients were used in different amounts and the catalyst compositionafter calcination is shown in Table 3. The catalysts of Examples 22-27were tested according to the same method of the above examples. Theamount of α-methyl styrene (AMS) in the product was measured and isshown in Table 3 as ppmw relative to the weight of the condensed productstream from the dehydrogenation reactor. The α-methyl styrene levelswere tested by gas chromatograph at the T70 temperature. Example 22depicts the average results for three catalysts with the samecomposition.

TABLE 3 Composition, millimoles/mole Exam- iron oxide Calc T70 S70 AMSple Ag Mo Ce Ca K T ° C. ° C. % ppmw 22 0 18 122 25 623 950 595.9 95.5260 (Comp) 23 70 18 125 25 623 975 588.1 95.8 226 24 70 18 125 25 6231035 590.0 96.4 248 25 100 18 150 25 623 1035 592.8 95.8 218 26 150 18150 25 623 1035 594.9 95.8 235 27 200 18 150 25 623 1035 588.7 96.2 225

As can be seen from Examples 22-27, an iron oxide based dehydrogenationcatalyst containing silver can result in the production of a reducedamount of alpha-methyl styrene impurity in an ethylbenzenedehydrogenation process.

One skilled in the art can vary many of the variables shown above inaddition to other variables to achieve a dehydrogenation catalyst thatis most effective for a particular application. Additional catalystcomponents may also be added to affect the properties and performance ofthe catalyst. The catalyst manufacturing process may be altered withrespect to such variables as drying times and temperatures, calcinationtimes and temperatures, and processing speed to affect the propertiesand performance of the catalyst.

1. A dehydrogenation catalyst comprising an iron oxide, an alkali metalor compound thereof, and silver or a compound thereof wherein the silveror compound thereof is present in an amount of at least about 0.01millimoles of silver per mole of iron oxide, calculated as Fe₂O₃.
 2. Acatalyst as claimed in claim 1 wherein the silver or a compound thereofis present in an amount of from about 0.25 to about 500 millimoles ofsilver per mole of iron oxide, calculated as Fe₂O₃.
 3. A catalyst asclaimed in claim 1 wherein the silver or a compound thereof is presentin an amount of from about 1 to about 300 millimoles of silver per moleof iron oxide, calculated as Fe₂O₃.
 4. A catalyst as claimed in claim 1wherein the silver or a compound thereof is present in an amount of fromabout 10 to about 100 millimoles of silver per mole of iron oxide,calculated as Fe₂O₃.
 5. A dehydrogenation catalyst comprising ironoxide, an alkali metal or compound thereof, silver, and silver ferrite.6. A catalyst as claimed in claim 1 wherein the alkali metal or compoundthereof comprises potassium.
 7. A catalyst as claimed in claim 1 whereinthe catalyst further comprises a lanthanide or a compound thereof.
 8. Acatalyst as claimed in claim 7 wherein the lanthanide or compoundthereof comprises cerium.
 9. A catalyst as claimed in claim 1 furthercomprising an alkaline earth metal or compound thereof.
 10. A catalystas claimed in claim 9 wherein the alkaline earth metal or compoundthereof comprises calcium.
 11. A catalyst as claimed in claim 1 furthercomprising a Column 6 metal or compound thereof.
 12. A catalyst asclaimed in claim 11 wherein the Column 6 metal or compound thereofcomprises molybdenum.
 13. A dehydrogenation catalyst comprising ironoxide, potassium or a compound thereof, cerium or a compound thereof,calcium or a compound thereof, molybdenum or a compound thereof andsilver.
 14. A catalyst as claimed in claim 1 wherein the catalystfurther comprises a metal selected from the group consisting ofpalladium, platinum, ruthenium, osmium, rhodium, iridium, titanium andcopper.
 15. A catalyst as claimed in claim 1 wherein the iron oxidecomprises regenerator iron oxide formed by the heat decomposition of aniron halide.
 16. A catalyst as claimed in claim 1 wherein the iron oxideis restructured by heat treating in the presence of a restructuringagent.
 17. A process for preparing a dehydrogenation catalyst comprisingpreparing a mixture of an iron oxide, an alkali metal or compoundthereof, and silver or a compound thereof wherein the silver or acompound thereof is present in an amount of at least about 0.01millimoles of silver per mole of iron oxide, calculated as Fe₂O₃ andcalcining the mixture.
 18. A process as claimed in claim 17 wherein thesilver compound is selected from the group consisting of silver oxide,silver chromate, silver ferrite, silver nitrate, and silver carbonate.19. A process for preparing a dehydrogenation catalyst comprisingpreparing a mixture of iron oxide, potassium or a compound thereof,cerium or a compound thereof, calcium or a compound thereof, molybdenumor a compound thereof and silver and calcining the mixture.
 20. Aprocess as claimed in claim 17 further comprising adding an alkalineearth metal or compound thereof to the mixture.
 21. A process as claimedin claim 17 further comprising adding a Column 6 metal or compoundthereof to the mixture.
 22. A process as claimed in claim 17 wherein thecalcining is carried out at a temperature of from about 600° C. to about1300° C.
 23. A process as claimed in claim 17 wherein the calcining iscarried out at a temperature of from about 750° C. to about 1200° C. 24.A process as claimed in claim 17 wherein the calcining is carried out ata temperature greater than 800° C.
 25. A process for dehydrogenating adehydrogenatable hydrocarbon comprising contacting a feed comprising adehydrogenatable hydrocarbon with a catalyst comprising an iron oxide,an alkali metal or compound thereof, and silver or a compound thereofwherein the silver or compound thereof is present in an amount of atleast about 0.01 millimoles of silver per mole of iron oxide, calculatedas Fe₂O₃.
 26. A process as claimed in claim 25 wherein the catalystcomprises silver and silver ferrite.
 27. A process for dehydrogenating adehydrogenatable hydrocarbon comprising contacting a feed comprising adehydrogenatable hydrocarbon with a catalyst comprising iron oxide,potassium or a compound thereof, cerium or a compound thereof, calciumor a compound thereof, molybdenum or a compound thereof and silver. 28.A process as claimed in claim 25 wherein the dehydrogenatablehydrocarbon comprises ethylbenzene.
 29. A process as claimed in claim 25wherein the feed further comprises steam.
 30. A process as claimed inclaim 29 wherein the steam is present in the feed at a molar ratio offrom 0.5 to 12 moles of steam per mole of dehydrogenatable hydrocarbon.31. A process as claimed in claim 29 wherein the steam is present in thefeed at a molar ratio of from 1 to 6 moles of steam per mole ofdehydrogenatable hydrocarbon.
 32. A method of using a dehydrogenatedhydrocarbon for making polymers or copolymers, comprising polymerizingthe dehydrogenated hydrocarbon to form a polymer or copolymer comprisingmonomer units derived from the dehydrogenated hydrocarbon, wherein thedehydrogenated hydrocarbon has been prepared in a process for thedehydrogenation of a dehydrogenatable hydrocarbon as claimed in claim25.